Speaking of the strongest short-lived euphoria, diethyl ether takes the prize, so that be 10/10 for reference. Opioids come a close (yet fairly distinct) second with 9/10 for both momentary and lasting euphoria. One HBWR trip was a solid 12/10, but I haven't been able to reproduce it since so there's that. Alcohol is a pitiful 2/10 even though it's my strongest addiction to date.